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    <title>Document</title>
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<script>
    let arr = [1, 2, 3, 4, 45]

    //  for in 是给对象提供的
    for (const key in arr) {
        console.log(key)
    }


    // for of 才是给数组提供的
    for (const item of arr) {
        console.log(item)
    }

    const a = {
        a: 1
    }
    const b = {
        b: 2
    }



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